10.5x13 vs 12.5x8

[bigjim2]

I have a 15' Sylvan fiberglass deck boat 1200#. running a Merc 50hp, currently running a 10.5x13 and struggles out of the hole, top speed once wot is achieved is acceptable. Only produce 5000 rpm trimmed out, will a 12.5x8 help get on plane quicker? there is no lower pitch available in a 10.5" prop

 

[WesNewell]

Of course an 8p prop will get on plane faster than a 13p, and will raise your rpm's to about 6000. Personally, I wouldn't go below a 10p prop unless you plan on pulling skiers. Which 50hp merc do you have? If it's a 4s, you can easily increase power to 60hp in most cases by removing the air intake restricter plate.

 

[bigjim2]

2 stroke, and I thought you need to change carbs to boost hp? is the restricter plate in the air box? yes dropping to an 8 pitch but increasing the wheel size by 2" to a 12.5", didnt know if that will give me what I want, get me out of the hole quicker but increase top rpm's enough to keep similar top speed?

 

[WesNewell]

Don't know much about the 2s, but rpm range is 5000-5500, so I wouldn't go below 11p if you're turning 5000 rpm now under normal use with a 13p prop. The mercury prop selector recommends a 12.35P prop for you type boat with 2000 50 hp classic. If your engine has a restricter plate removing it might increase power and allow you to stay with your current 13p prop.

 

[bigjim2]

Do you know where the restricter plate is located?

 

[WesNewell]

I don't even know if it has one. That's why I said IF it did. All i know is it's the same displacement as the 60hp engine 967cc iirc and the restricter plate would be somewhere in the air intake area. If you can find a parts breakdown for your engine, you could look there. I know where they are on the 4s models, You might ask in the Mercury outboard motors forum. Make sure you specify 2s year and model.

 

[GA_Boater]

Do you know where the restricter plate is located?

Wes is talking about a 4 stroke, so it doesn't apply to your 2 stroke.

Look up the specs for your 50 and compare with a 60 of the same year. I think you'll find it's more than carbs and the displacement may larger.